I haven't looked too closely at Lit source code recently so I couldn't really comment on that but, from a high level, they differ in the sense that lit uses render function (like react) that mixes HTML/JS whereas synergy separates the two between view/template. Neither is better or worse of course, its all about trade-offs and preferences. Lit elements are described with classes whereas synergy uses factory functions. Lit uses Shadow DOM by default, whereas synergy makes it optional.

That’s a very nice summary. Thanks for this clarification.